\input pstfig
$
\def\myr{2}
\def\myR{3}
\pnode(0,0){O}
\pscircle(O){\myr}
\pscircle(O){\myR}
\thinline
\psline(O)(\myR; 90)
\thinline
\psbrace[nodesepA= 0.2ex,linewidth=0.4pt,ref=lC](L)(\myR; 90){R}
\psbrace[nodesepA=-0.2ex,linewidth=0.4pt,ref=rC,rot=180](\myr; 90)(L){r}
$
\bye
